The rules for mounting a creature say "A willing creature that is at least one size larger than you and that has an appropriate anatomy can serve as a mount." So a Medium-sized creature, like a Human, can ride on a willing creature that is Large-sized or bigger.

A Mule is Medium-sized, but has a "Beast of Burden" ability: "The mule is considered to be a Large animal for the purpose of determining its carrying capacity."

Does this counting as Large for "carrying capacity" also mean that it counts as large for purposes of being ridden as a mount? It sure seems that logically a human ought to be able to ride a Mule, and I may allow it in games I DM simply on that basis, but I'm not sure where in the rules it's explicitly said.

I think a big part of my confusion is that carrying capacity seems to be defined in the list of mounts in the Equipment chapter. There it says that a mule's carrying capacity is 420 lb., and creature carrying capacity doesn't seem to be related to creature size at all. So I'm not sure what the "Beast of Burden" ability is supposed to mean at all.

2 Answers
2

A medium character can probably ride a mule awkwardly, but only a small or tiny character can effectively use a mule as a mount in combat.

The Beast of Burden ability explicitly states exactly what game mechanic it affects - how much weight the mule can carry. It doesn't have any effects beyond that. The mule is strong enough to carry most medium-sized creatures, and that's probably good enough for transportation purposes, but it's just too small for them to be able to effectively ride it as a mount in combat.

Carrying Capacity. Your carrying capacity is your Strength score multiplied by 15. This is the weight (in pounds) that you can carry, which is high enough that most characters don't usually have to worry about it.

...

Size and Strength. Larger creatures can bear more weight, whereas Tiny creatures can carry less. For each size category above Medium, double the creature's carrying capacity and the amount it can push, drag, or lift. For a Tiny creature, halve these weights.

The mule, as medium creature with a strength of 14, would normally have a carrying capacity of 210lbs - but because its special ability means it is treated as large for the purpose of determining carrying capacity, that value is doubled to 420lbs (the value given for the mule in the mounts table).

It may be worth keeping in mind that horses/donkeys/mules are creatures with considerable variation of size between individuals/breed - wikipedia suggests that weight can range between a mere 50lbs to over 1000lbs. One creature stat block will never accurately describe all of them (you may note there are several different varieties of horse to choose from in the creature lists, including the much smaller pony). Whilst we can easily imagine a mule big enough to serve as a combat mount for a human, and such mules undoubtedly exist in the real world - that's not the mule as described by the Mule creature stat block, which presumes a relatively small equine. A larger mule should probably be represented using the statistics for an equivalent horse - the fact that it is actually a mule is not important for the mechanics of the game.

\$\begingroup\$Mules are amazing beasts of burden, smarter and tougher then a horse, larger and stronger then a donkey. Many mules are the same size as a horse.\$\endgroup\$
– Garret GangJun 25 '18 at 13:24

\$\begingroup\$Looking at mule forms, equine are measured for height in hands (1 hand =4") Though you can cross a mule with a pony, making a small mule, most people think of mules having the height between 15 and 16 hands (60-64" to the shoulder) They can and have carried many medium-sized humanoids (For an example, look up Festus Haggin)\$\endgroup\$
– Victor BMar 19 at 23:32

Yes. People do it all the time.

First of all, "logically, it seems like a human could do this" is a sufficient answer under the rules.

Second, as you observe, the mule is listed as a mount. Now, so is the mastiff, but the mastiff's description clarifies that it's used as a mount by Small races. The mule says no such thing.

Third, carrying capacity actually is related to creature size. For a Medium creature, it's 15 lb per Strength point. Each size step up multiplies that by 2. So a Str 14 human would be able to carry 210 lbs (not enough for a Medium rider with gear and provisions) but the mule is treated as Large, so it can easily carry a rider.

(I suspect that this is why Beast of Burden says to treat the creature as Large, rather than just to double its weight limit: so that we know that it's a suitable mount for a Medium creature.)

\$\begingroup\$I'm afraid "logically, it seems like a human could do this" is not a reason to permit a human do to something under the rules. For example, a human can survive for 30 days or more without food before dying of starvation (provided they are well hydrated). But the rules will kill a human with a Con of 20 after 14 days without food (PHB, p. 185 & 291).\$\endgroup\$
– GandalfmeansmeJun 27 '18 at 0:41

\$\begingroup\$I also believe you are misrepresenting the text of "Beast of Burden." It says "The mule is considered to be a Large animal for the purpose of determining its carrying capacity." You suggested that the rules did not limit this to its "weight limit" (carrying capacity), when they explicitly did exactly that.\$\endgroup\$
– GandalfmeansmeJun 27 '18 at 0:50

\$\begingroup\$And as a better example of "logically, it seems like a human could do this" being a tricky metric, also consider that most humans could successfully strike more than one person within six seconds (if they were all next to the striker). But a first level fighter cannot hit several enemies with one attack, just because "logically, it seems like a human could do this."\$\endgroup\$
– GandalfmeansmeJun 27 '18 at 0:52

\$\begingroup\$@Gandalfmeansme But I think it's perfectly within a DM's role to rule that "yeah, that makes sense, go ahead" even if it contradicts rules-as-written. It's good for the DM to know why the rules are set up as they are, and to understand that there may be other implications as one bends and breaks rules, but playing D&D with a more story-centric rather than rules-centric approach is a perfectly reasonable choice depending on the group.\$\endgroup\$
– Peter Cooper Jr.Jun 27 '18 at 13:24

\$\begingroup\$@PeterCooperJr. The DM can definitely break any rule they want at any time. But the statement I am objecting to is "'logically, it seems like a human could do this' is a sufficient answer under the rules." To me, this answer implies that the rules themselves are defined by common sense, which they are not.\$\endgroup\$
– GandalfmeansmeJun 27 '18 at 13:35